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Ch. 16: The Molecular Basis of Inheritance - Coggle Diagram
Ch. 16: The Molecular Basis of Inheritance
DNA as the Genetic Material
Griffith Experiment
Transformation
Harmless + heat-killed harmful --> harmful cells
Avery, McCarty, MacLeod
DNA is transforming substance
Hershey–Chase Experiment
DNA enters bacterium
Protein does not
Chargaff’s Rules
A = T
G = C
Base ratios vary by species
Structure of DNA
Double Helix
Two antiparallel strands
Complementary base pairing
Nucleotides
Sugar
Phosphate
Nitrogenous base
Base Types
Purines: A, G
Pyrimidines: C, T
Base Pairing
Backbone
Sugar-phosphate
Antiparallel 5′ --> 3′ orientation
Rosalind Franklin
X-ray diffraction
Helical structure evidence
DNA Replication
Replication Fork
Site where DNA strands separate
Primase
Makes RNA primer
Tells polymerase where to start
DNA Polymerase
Adds DNA bases to 3′ end
Works 5′ --> 3′
Proofreads errors
Helicase
Unzips DNA
Topoisomerase
Relieves twisting strain
Unwinds DNA ahead of fork
Leading Strand
Continuous synthesis toward fork
Lagging Strand
Away from fork
Okazaki fragments
Requires multiple primers
DNA Ligase
Connects Okazaki fragments
Seals sugar-phosphate backbone
DNA Repair
Mismatch Repair
Enzymes replace incorrectly paired nucleotides
Nucleotide Excision Repair
Nuclease cuts out damaged DNA
DNA polymerase replaces section
DNA ligase seals it
Proofreading
Performed by DNA polymerase
Telomeres
Function
Protect gene regions
Prevent erosion of coding sequences
Telomerase
Extends telomeres in germ cells
Often active in cancer cells
Aging
Telomeres shorten over time
Chromosome / DNA Packaging
Chromatin
DNA + protein complex
Histones
Core proteins
DNA wraps twice around each
Nucleosome
“Beads on a string”
Levels of Packing
10-nm fiber
30-nm fiber
Looped domains
Condensed metaphase chromosome
Euchromatin
Loosely packed
Actively expressed
Heterochromatin
Densely packed
Gene-poor or silent regions